1. Field of the Invention
The present invention relates to a digital camera based on an image sensor, such as a CCD (Charge Coupled Device) or a CIS (CMOS Image Sensor). More particularly, the present invention relates to a method and apparatus for minimizing deterioration of a photographed image caused by user's hand-trembling when photographing using such a digital camera.
2. Description of the Related Art
When a user photographs an image using a digital camera, a hand-trembling phenomenon may occur in the photographed image by user's hand-trembling or unintended movement. There has been research previously conducted on various methods for compensating such a trembling phenomenon. Technologies for compensating such a hand-trembling phenomenon generally employed in the prior art are classified into three technologies, i.e., DIS (Digital Image Stabilization), EIS (Electronic Image Stabilization), and OIS (Optical Image Stabilization). The features of these conventional methods are summarized in Table 1.
TABLE 1TechDetection ofImageAdvantageDisadvantageRelated KRHand-CompensatingUnexaminedTrembling PatentPublicationNos.DISComparingImageSmall sizeLarge amount1996-two continuedprocessingLow costof calculation0036545imagesLongphotographingtimeDeterioration ofimage qualityEISEmployingImageMedium orDeterioration of1996-movementprocessingsmallimage0020371detectionsizequality2004-means, suchShort0082645as gyro-sensorphotographingtime ascompared toDISOISEmployingOpticalHigh image Large sizeLensmovementSystemqualityHigh costmovementdetectionCompensatingApplicable totechnology:means, suchstill image2006-0071224as gyro-sensorSmallSensoramount ofmovementcalculationtechnology:2006-004003
As indicated in Table 1, the OIS technology is advantageous in that it is also applicable to still image compensation and is expected to provide a high image quality after compensation. With the OIS technology, however, it is essential to add movement detection means, such as gyro-sensor for detecting the amount of hand-trembling, and an optical correction means for compensating the hand trembling detected by the movement detection means. Therefore, high costs and increased size are inevitable with the OIS technology. Examples of such a technology include Korean Un-examined Patent Publication No. 2006-0071224 entitled “Image Stabilizer for Camera” of Hong-Seok Lee et al., which was filed in the name of Samsung Electronic Co., Ltd. on Dec. 21, 2004, and Korean Un-examined Patent Publication No. 2006-004003 entitled “Apparatus for Compensating Hand-Trembling in Camera Lens Assembly” of Jun-Mo Koo, which was filed in the name of Samsung Electronic Co., Ltd. on Nov. 4, 2004.
Compared to the OIS technology, the DIS technology can assure low H/W cost and small size since detection and compensation of hand-trembling are both achieved by image processing. However, the DIS technology has a problem in that the time the camera requires for photographing the image is relatively long due to the increased amount of calculation, which results from the employment of an image processing S/W for detecting the amount of hand-trembling and for compensating an image. Thus, there is difficulty in capturing an image that quickly changes, as well as having person posing for the additional time required.
Currently available hand-trembling compensating technologies employing an image processing S/W include pixel data movement, a synthesis of multiple short-time exposure images, synthesis of a long-time exposure image with a short-time exposure image, application of an image-trembling compensating filter, etc.
However, due to shortcomings of software technologies developed up to now, deterioration of image quality is inevitable. An example of such a technology is disclosed in Korean Un-examined Patent Publication No. 1996-0036545 entitled “Apparatus for Compensating Hand-Trembling of Camcorder” of Young-Cheol Park, which was filed in the name of Samsung Electronic Co., Ltd. on Mar. 30, 1995.
The EIS technology combines the above-mentioned DIS technology and OIS technology in such a manner that the detection of an amount of hand-trembling is performed using a movement detection means, such as a gyro-sensor, and the compensation of an image is performed using an image processing S/W. As a result, with the EIS technology, it is possible to expect that a result of a middle level between the DIS technology and the OIS technology can be obtained in terms of the length of time and costs for image-capturing, the size of H/W, etc.
However, EIS technology has a disadvantage in that a substantially degraded image is obtained as compared to the OIS because it employs an image processing S/W like the DIS technology. Examples of such a technology includes Korean Un-examined Patent Publication No. 1996-0020371 entitled “Method and Apparatus for Compensating Hand-Trembling of Camcorder” of Nam-Soo Lee, which was filed in the name of LG EI on Nov. 21, 1994, and Korean Un-examined Patent Publication No. 2004-0082645 entitled “An Image Acquisition System Capable of Obtaining Stabilized Image and Method of Stabilizing Image” of Yong-Cheol Cho, which was filed in the name of Samsung Electronic Co., Ltd. on Mar. 19, 2003.
Beyond the above-mentioned hand-trembling compensating technologies, also known is an increasing sensitivity of an image sensor (e.g. change ISO 100 into ISO 400 with regard to the sensitivity of an image sensor) so as to reduce exposure time, thereby avoiding hand-trembling problems, and a remote exposure button technology employing a remote controller for exposing a shutter so as to reduce the hand-trembling effect. However, the increasing sensitivity of an image sensor has a problem in that image quality is deteriorated due to noise, and the remote exposure button technology has a problem in that user's convenience is made worse, and it is impossible to avoid hand-trembling caused by an action beyond shutter pressing.
In addition, the best picture function, which provides a number of pictured images so as to allow a user to choose one or more desired pictures, may be considered as conducting a role of reducing hand-trembling problems. However, with this technology, a user's inconvenience is caused because the user must select the image from one or more photographs. Furthermore, it is difficult for the user to determine a hand-trembling level and to choose images pictured without hand-trembling from high-pixel images displayed through a small LCD window.
Consequently, there is a need in the art to provide a technology of minimizing deterioration of image quality caused by hand-trembling without deteriorating a user's convenience.